Fats and prostate cancer.

Vegetarian diets are often low in a group of fats called omega-3 fatty acids. Fats in this group include alpha-linolenic acid (found in flax seeds and flax seed oil and, to a smaller extent, in canola oil and soy products), docosahexaenoic acid (DHA, found in fatty fish), and eicosapentaenoic acid (EPA, also found in fatty fish). Omega-3 fatty acids have been associated with a reduced risk of heart disease and may have other health benefits. Since vegetarians do not eat fatty fish, they have been encouraged to include sources of alpha-linolenic acid like flax seeds and flax seed oil in their diets regularly.

A new report raises questions about alpha-linolenic acid for some men. A study of more than 45,000 men in the U.S. found that those men whose diets were highest in alpha-linolenic acid did not have an increased risk of developing prostate cancer in general but did have an increased risk of developing advanced prostate cancer. This was true whether the alpha-linolenic acid came from meat and dairy products or from salad dressing and margarine (flax seed or flax seed oil intake was not reported). The other omega-3 fatty acids, EPA and DHA, were associated with lower prostate cancer risk. We cannot be sure that the same results would be seen in vegans because they frequently use sources of alpha-linolenic acid that were not examined in this study. However, until more information is available, the results of this study suggest that men who are at increased risk of prostate cancer should not use high amounts of alpha-linolenic acid. Some vegetarian men may opt to use a vegan DHA supplement derived from microalgae instead of other sources of omega-3 fatty acids.

Leitzmann MF, Stampfer MJ, Michaud DS, et al. 2004. Dietary intake of n-3 and n-6 fatty acids and the risk of prostate cancer. Am J Clin Nutr 80:204-16.